October 11, 2012
It’s well established that, in the years to come, increasing amounts of carbon dioxide in the air will cause the climate to change, thereby leading to the ice caps melting at an accelerated rate and worldwide sea level rise. A new scientific finding, though, points at a troubling, entirely separate direct effect of carbon on ice—one that has nothing to do with warming at all.
As documented in a study published yesterday in the Journal of Physics D, researchers from MIT have discovered that merely being in the presence of increased concentrations of carbon dioxide causes ice to significantly weaken, with reduced material strength and fracture toughness, regardless of temperature. With enough carbon dioxide in the air, this alone could make glaciers more likely to split and fracture. Add in the fact that global temperatures will continue to warm—especially around the poles—and the combination of these two factors could mean that the ice caps will melt at even faster rates than experts have previously projected.
“If ice caps and glaciers were to continue to crack and break into pieces, their surface area that is exposed to air would be significantly increased, which could lead to accelerated melting and much reduced coverage area on the earth,” said the study’s lead author, Markus Buehler. “The consequences of these changes remain to be explored by the experts, but they might contribute to changes of the global climate.”
Buehler and his co-author, Zhao Qin, used computer simulations at the atomic level to evaluate the dynamics of ice strength in the presence of various concentrations of carbon dioxide. They found that the gas diminishes the strength of ice by interfering with the hydrogen bonds that hold together the water molecules in an ice crystal. Specifically, at the atomic level, the carbon dioxide competes with the bonded water molecules and, at high enough concentrations, displaces them from the bonds and takes their place.
The carbon dioxide molecules start infiltrating a piece of ice at an outer edge, then slowly split it apart by migrating inward as a crack forms. In doing so, they also attract water molecules outward to the edge by forming bonds with the water molecules’ hydrogen atoms, leaving broken bonds within the crystalline structure and decreasing the ice’s strength overall. The simulations showed that ice that has been infiltrated with carbon dioxide to the point that the gas occupies two percent of its volume is roughly 38 percent less strong.
“In some sense, the fracture of ice due to carbon dioxide is similar to the breakdown of materials due to corrosion, e.g., the structure of a car, building or power plant where chemical agents ‘gnaw’ at the materials, which slowly deteriorate,” Buehler told Environmental Research Web. Since glaciers typically begin to break apart with the formation of small cracks, the researchers say, this could lead to further large-scale fractures, such as the one that recently occurred in Antarctica and produced a fragment larger than New York City.
Because the finding is the first evidence of this phenomenon, it’s too early to say just how much it will accelerate ice melt beyond previous predictions. There are several mechanisms, though, by which it could lead experts to revise upward their estimates for ice melt and sea level rise given a continued increase in greenhouse gas emissions.
In addition to the obvious—that warmer air plus weaker ice means a faster rate of melting—there is the fact that the ice caps play a crucial role in reflecting sunlight back into space. Currently, they cover roughly seven percent of the earth’s surface but are responsible for reflecting 80 percent of the sun’s rays. This is because ice’s bright white color helps it reflect light more efficiently than nearly any other type of ground cover.
If increased carbon dioxide concentrations and warmer temperatures cause ice to melt unexpectedly quickly, though, this bright white ice will be replaced by dark ocean water. More and more sunlight would enter and stay in the atmosphere, thereby causing more and more warming. This positive feedback loop could constitute one of the dreaded “tipping points” that climatologists fear might send our climate on an uncontrolled path towards calamity.
Since the paper only deals with ice at the microscopic level, the next step would be testing the effect of increased carbon dioxide concentrations on ice in a lab setting to check if the effects of the simulated model hold true. Of course, if nothing changes in terms of carbon emissions, we might well have the chance to see if these effects occur on a much larger scale—in the world’s glaciers and polar ice caps.
Sign up for our free email newsletter and receive the best stories from Smithsonian.com each week.